Beyond Simple Exponential Correlation Functions and Equilibrium Dynamics in X-Ray Photon Correlation Spectroscopy

We discuss the complex dynamics in condensed matter studied with x-ray photon correlation spectroscopy (XPCS) in which non-exponential correlation functions and dispersion relations deviating from the simple diffusion law are observed. Results are presented for two systems whose dynamics are characterized by compressed, faster-than-exponential correlation functions associated with hyper-diffusive motion. In the first case, the microscopic response of an aerogel following sectioning is investigated. In the second, the out-of-equilibrium dynamics in a dense colloidal gel recovering from shear is analyzed. In both cases, the dynamics, which can be associated with relaxation of internal stress, exhibits ageing. Included in the analyses are calculations of two-time correlation functions and the variance of the instantaneous degree of correlation, yielding the dynamical susceptibility

XPCS Investigation of the Dynamics of Filler Particles in Stretched Filled Elastomers.

International audienceThe complexity of the mechanical behavior of filled elastomers can be partly attributed to the fact that the duration of an applied strain plays a crucial role. In order to bring new insights into this still incompletely solved problem, we look for relationships between the macroscopic mechanical relaxation and the relaxation of the filler particles at the nano-to mesoscale. To this end, X-ray photon correlation spectroscopy (XPCS) in homodyne and heterodyne configurations combined with tensile stress relaxation is employed. The paper is devoted to the study of the role of the filler filler and the filler matrix interactions in a cross-linked,elastomer on the aging mechanisms under strain. The fillers investigated are carbon black, as an example of strong filler matrix interactions, and hydroxylated silica for which the filler filler interaction is strong (H-bonds). Homodyne XPCS correlation reveals features of jammed systems (compressed exponential and ballistic motion) for both systems. The exponents characterizing the aging of the homodyne relaxation times are not the same in the carbon black and in the silica filled samples. For both systems, the decrease of the particle velocity determined by heterodyne detection with aging time follows a power law. The silica sample is characterized by a slow decrease of the velocity during aging. For the carbon black sample, the velocity remains small and decreases faster than for the silica sample. The reverse is observed for the behavior of the tensile force

Antimicrobial Peptides of Lactic Acid Bacteria: Mode of Action, Genetics and Biosynthesis.

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